Allow keepalives on status port

[rohansingh]

What this PR does / why we need it:

A few years ago, #3684 changed the status port to use Unix sockets rather than TCP. As part of that change, keepalive_timeout 0 was added.

Sometime later, #4487 changed the status port back to TCP. However, keepalive was never re-enabled.

In practice we're seeing behavior where nginx stops accepting GET or POST to the status port during graceful shutdown since new connections aren't allowed.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] CVE Report (Scanner found CVE and adding report)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation only

How Has This Been Tested?

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I've read the CONTRIBUTION guide
• [ ] I have added unit and/or e2e tests to cover my changes.
• [ ] All new and existing tests passed.